Combination of silica and graphite and its use for decreasing the thermal conductivity of vinyl aromatic polymer foam

ABSTRACT

The invention relates to the co-use of a) a certain type of silica and b) a certain type of graphite, wherein the silica and the graphite are used in a weight ratio in a range of from 1:1 to 1:10, for decreasing the thermal conductivity of vinyl aromatic polymer foam.

This application is the U.S. national phase of International ApplicationNo. PCT/EP2016/050627 filed 14 Jan. 2016, which designated the U.S. andclaims priority to EP Patent Application No. 15461506.6 filed 14 Jan.2015, the entire contents of each of which are hereby incorporated byreference.

The present invention relates to the use of a) a certain type of silicain combination with b) a certain type of graphite, for decreasing thethermal conductivity of vinyl aromatic polymer foam. The invention alsorelates to processes for the preparation of expandable polymergranulates and the expandable polymer granulate. The invention furtherrelates to vinyl aromatic polymer foam and to a masterbatch comprisingthe mixture of a) with b).

Vinyl aromatic polymers are known and are used for the preparation ofexpanded products that are adopted in a variety of applications, ofwhich the most important one is for thermal insulation. This is whythere is a continuously increasing demand for expanded vinyl aromaticpolymers with low thermal conductivity as well as good mechanical andself-extinguishing properties.

It is generally known that the addition of athermanous additives fromthe group of heat absorbers (e.g. carbon black), heat scatterers (e.g.minerals from the group of silicas and titanium oxides) and heatreflectors (e.g. aluminium pigment and graphite) decreases the thermalconductivity of vinyl aromatic polymer foams. Examples for such types ofpolymers are those obtained by suspension polymerization of vinylaromatic monomers (in particular of styrene) and optionally comonomers.Other examples for such type of polymers are those obtained by theextrusion of general purpose polystyrene or its copolymers.

Typically, the addition of a combination of athermanous additives thatcan absorb or scatter heat radiation to prolong the IR rays' pathwayresults in a significant decrease of thermal conductivity. However, theaddition of IR reflectors results in the most advantageous effect. Acombination of IR scatterers and IR reflectors can influence thereduction of the concentration of typical IR absorbers (such as carbonblack) and leads to an improvement of the self-extinguishing effect ofpolystyrene foams. However, an addition of carbon black, especially inextrusion processes, requires the addition of a relatively high amountof brominated flame retardant, to maintain acceptable self-extinguishingproperties, e.g. suitable performance for passing the flammability testaccording to the German industry standard DIN 4102 (B1, B2).

Poor thermal stability of foams made of vinyl aromatic polymers filledwith carbon-based athermanous additives is also a problem. Such foams,having black or grey colour, absorb a relatively high amount of heatenergy, thus the insulation boards made thereof and applied on buildingwalls can shrink or deform significantly. Thus, the insulationperformance may deteriorate. Finally, when trying to create an optimumcell structure with a narrow cell size distribution, in order to obtainmaterials with significantly decreased thermal conductivity, severalproblems were identified when using carbon black, graphite or especiallymineral athermanous additives, because these additives also act asnucleating agents and have a negative effect on bubble formation.

On the other hand, the presence of small amounts of athermanous fillersof the heat scatterer type does not result in a substantialdeterioration of the flame retarded polymer foam's self-extinguishingproperties. Rather, these properties are improved, but the decrease ofthe foam's thermal conductivity is not as pronounced as it would be infoams comprising carbon-based additives, i.e. comprising athermanousadditives of the heat absorber or of the heat reflector type (inparticular carbon blacks and/or graphites).

WO 2006/058733 A1 teaches expandable styrene polymer granulatescontaining a) filler selected from the group of inorganic powdermaterials (such as silicic acid) and b) carbon black or graphite. Theamount of a) filler is 5 to 50 wt. %, and the amount of b) carbon blackor graphite is 0.1 to 10 wt. %. The filler of WO 2006/058733 A1 has anaverage particle diameter in a range of from 1 to 100 μm.

WO 2008/061678 A2 discloses the use of carbon black having a specificelectric conductivity, and optionally graphite, to decrease the thermalconductivity of expandable vinyl aromatic polymers.

WO 2012/024708 A1 teaches polymer foams containing carbon-basedathermanous particles. The carbon of the athermanous particles ispartially arranged in a graphitic manner and is also present asturbostratic carbon.

EP 0 620 246 A1 teaches the use of athermanous materials in polystyrenehard foam (EPS or XPS). Examples for athermanous materials are metaloxides (such as Fe₂O₃ or Al₂O₃), non-metal oxides (such as SiO₂), metalpowder, aluminium powder, carbon (such as carbon black, graphite or evendiamond), or organic colorants or colorant pigments.

JP 63183941 teaches the use of aluminium pigment, titanium dioxide andgraphite, having specific particle size and heat radiation reflectivity,to decrease the thermal conductivity of polystyrene foams. The silicapowder used in Example 6 as listed in Table 1 of JP 63183941 has anaverage particle size of 3.2 μm.

EP 1 159 338 A teaches expandable polystyrene (EPS) containing aluminiumparticles and optionally graphite. Further, EP 0 863 175, EP 0 981 574,EP 1 758 951, DE 198 28 250 A1, WO 98/51734 A1, EP 1 031 600 A2, EP 1661 940 A1, WO 02/055594 A1 and EP 1 771 502 A2 teach the use ofgraphite in polystyrene foams.

US 2012/0091388 A1 discloses expanded vinyl aromatic polymers comprisinga. graphite, b. optional self-extinguishing brominated additive, c.optional synergist for b., and d. optional inorganic additive. Anexample for d. inorganic additive is silicon oxide (such as aerosilica).The BET surface of a typical aerosilica is well above 100 m²/g, and theparticle size is well below 10 nm. When using aerosilica for example inan extrusion process for the production of expandable vinyl aromaticpolymer granulate, it is impossible to stabilize the process even in thepresence of small amounts of aerosilica, e.g. below 1 wt. %: because ofaerosilica's very high BET, the resultant modification of rheology is sostrong that pressure increases dramatically, and it is not possible tostabilize the process and the granulate.

US 2007/112082 A1 discloses moldable-foam moldings whose density is inthe range from 8 to 200 g/l, obtainable via fusion of pre-foamed foambeads composed of expandable pelletized filled thermoplastic polymermaterials, and a process for preparing the expandable pelletized polymermaterials.

EP 2 025 961 A2 teaches a two-step process for the production ofexpandable polystyrene granulate. The process includes the mixing ofgraphite particles with a styrene-based resin and extruding thecomposition, and carrying out seed polymerization by suspending thegraphite-containing micropellets in water and adding styrene-basedmonomer.

WO 2012/024709 A1 teaches flame retarded expandable polymers containingsolid carbon-based additives containing sulphur, wherein the sulphurcontent is at least 2000 ppm. Examples for the solid additive areanthracite, coke and carbon dust.

A desired expanded polymer foam should contain athermanous filler(s) ofa type and in an amount that maintain the foam's self-extinguishing andmechanical properties in the same range as in an expanded polymerwithout such fillers, and that at the same time decrease the thermalconductivity of the foam.

It has now surprisingly been found in accordance with the presentinvention that the co-use of

-   -   a) a certain type of silica, in a specific amount, and    -   b) a certain type of graphite, in a specific amount,    -   decreases the thermal conductivity of vinyl aromatic polymer        foam (the decrease being measured in accordance with ISO 8301),        without adversely affecting the foam's flammability and        mechanical properties, and that this effect is particularly        pronounced if a) the type of silica and b) the type of graphite        are used in a weight ratio, i.e. a):b), in a range of from 1:1        to 1:10.

The present invention has the following aspects:

-   -   (I) the use of a) silica in combination with b) graphite, for        decreasing the thermal conductivity of vinyl aromatic polymer        foam;    -   (II) processes for the preparation of expandable polymer        granulate;    -   (III) expandable polymer granulate comprising one or more        propellants, a) silica, b) graphite, and c) vinyl aromatic        polymer;    -   (IV) expanded vinyl aromatic polymer foam comprising a)        silica, b) graphite, and c) vinyl aromatic polymer; and    -   (V) a masterbatch comprising a) silica, b) graphite, and c)        vinyl aromatic polymer.

DETAILED DESCRIPTION

In a first aspect, the invention relates to the use of a) a certain typeof silica in combination with b) a certain type of graphite, fordecreasing the thermal conductivity of vinyl aromatic polymer foam.

The polymer used in accordance with the invention is based on one (ormore) vinyl aromatic monomer(s), preferably styrene, and optionally oneor more comonomers, i.e. it is a homopolymer or a copolymer. The polymercomposition comprises, in addition to the polymer component, a) silicaand b) graphite, and typically and preferably a variety of furtheradditives, as set out below.

Silica

The silica as used in accordance with the invention is amorphous and hasthe following specific properties:

(i) a BET surface of from 1 to 100 m²/g and,

(ii) an average particle size in a range of from 3 nm to 1,000 nm.

The method to determine the silica's BET surface is preferably based onthe standards ASTM C1069 and ISO 9277 and is conducted as follows: inthe first step, 2 to 5 g of sample are dried at 105° C. and placed in adesiccator for cooling and further degassing. Subsequently, 0.3 to 1.0 gof the dry material is weighed into a test tube and placed in thedegassing unit for about 30 min. Afterwards, the sample is transferredto the measuring unit and is measured using the Micromeritics Tristar3000 instrument.

The silica as used according to the invention preferably has a BETsurface in a range of from 3 to 80 g/m², more preferably 5 to 70 m²/g,most preferably 8 to 60 m²/g, such as 10 to 50 m²/g, in particular 13 to40 m²/g, or 15 to 30 m²/g, such as about 20 m²/g.

Moreover, the silica as used according to the present invention isdefined by an average particle size, as measured according to theprocedure detailed below, of 3 nm to 1000 nm.

Average particle size in the description of the present invention meansmedian primary particle size, D(v, 0.5) or d(0.5), and is the size atwhich 50% of the sample is smaller and 50% is larger. This value is alsoknown as the Mass Median Diameter (MMD) or the median of the volumedistribution.

The method to determine the average particle size is conducted asfollows: in the first step, 45 g of distilled water and 5 g of sampleare placed into a beaker and stirred to allow the entire sample to bewetted. Subsequently, the sample is dispersed in an external ultrasonicprobe for 5 min at 100% amplitude. The measurement is performedautomatically using the primary agglomerate program in a MalvernMasterSizer 2000 device.

It is preferred that the average particle size of the silica as usedaccording to the present invention is within a range of 20 to 800 nm,preferably 30 to 600 nm, such as 40 to 400 nm, in particular from 100 to200 nm.

According to the present invention, the silica is present in an amountof from 0.01 to less than 2 wt. %, based on the weight of the polymer(inclusive of solid and, if any, liquid additives, but exclusive ofpropellant). Preferably, silica is present in an amount of 0.1 to 1.6wt. %, more preferably 0.5 to 1.5 wt. %, such as about 1.0 wt. %, basedon the weight of the vinyl aromatic polymer (inclusive of solid and, ifany, liquid additives, but exclusive of propellant).

The silica according to the invention is amorphous (i.e.non-crystalline) silicon dioxide, and the silica particles arepreferably spherically shaped.

It is most preferred that the silica a) as used according to the presentinvention comprises a Sidistar type of material from ELKEM, typicallywith an average primary particle size of about 150 nm and a low BETsurface area of about 20 m²/g, and most preferred is that a) is SidistarT120.

Graphite

The graphite as used in the invention has the following properties:

-   -   (i) a carbon content in a range of from 50 to 99.99 wt. % and    -   (ii) a particle size in a range of from 0.01 to 100 μm.

Preferably, the graphite's carbon content is in a range of from 95 to99.9 wt. % and more preferably over 99.5 wt. %. Preferably, the carboncontent is measured according to the method L-03-00A of the company GK.

The graphite as used according to the invention has a particle size in arange of from 0.01 to 100 μm, preferably as measured according to methodL-03-00 of the company GK, which is a laser diffraction method using aCilas 930 particle size analyzer equipment. It is preferred that theparticle size of the graphite as used according to the invention is from0.1 to 30 μm. The most preferred particle size range is from 0.5 to 25μm, in particular from 1 to 10 μm; specifically, for example, a range offrom 3 to 8 μm.

The graphite's mean particle size is preferably in a range of from 5 to7 μm, D90 in a range of from 7 to 15 μm, and D100 in a range of from 15to 20 μm.

The sulphur content of the graphite as used according to the inventionis preferably in a range of from 10 to 2000 ppm, as measured accordingto ASTM D1619, preferably from 100 to 1500 ppm, in particular from 400to 1000 ppm.

The ash content of the graphite as used according to the invention ispreferably in a range of from 0.01 to 2 wt. %, preferably from 0.1 to 1wt. %, in particular below 0.5 wt. %. The ash content is preferablymeasured according to method L-02-00 of the company GK.

The moisture content of the graphite as used according to the inventionis preferably in a range of from 0.01 to 1 wt. %, preferably from 0.1 to0.5 wt. %, in particular below 0.4 wt. %. The moisture content ispreferably measured according to a method of the company GK (L-01-00).

The graphite is present according to the invention in an amount of 0.01to 10 wt. %, based on the weight of the vinyl aromatic polymer(inclusive of solid and, if any, liquid additives, but exclusive ofpropellant), preferably in a range of from 1.0 to 8.0 wt. %, morepreferably in a range of from 1.5 to 7.0 wt. %, in particular in a rangeof from 2.0 to 6.0 wt. %, such as in a range of from 2.5 to 5.0 wt. %,e.g. in a range of from 3 to 4 wt. %.

Preferably, a) the silica and b) the graphite are used in a weight ratioa):b) in a range of from 1:1.5 to 1:8, more preferably a) the silica andb) the graphite are used in a weight ratio a):b) in a range of from 1:2to 1:5, most preferably a) the silica and b) the graphite are used in aweight ratio a):b) of about 1:3.

The best performance in foams in terms of

-   -   i) decrease of thermal conductivity (the decrease being measured        according to ISO 8301),    -   ii) increase in specific mechanical properties (the increase in        compressive strength and in bending strength being measured in        accordance with EN 13163) and    -   iii) improvement in self-extinguishing properties (the        improvement being measured in accordance with EN ISO 11925-2,        preferably, as measured in accordance with DIN 4102 B1, B2)        is achieved, accompanied by a reduction in the required content        of graphite, when specifically Sidistar T120 from Elkem is        present in combination with the natural graphite CR5995 from GK,        in a weight ratio of about 1:3. Then it is possible to reduce        the graphite content to about 3 wt. %, and to maintain the        thermal conductivity at the same level as if 5 to 6% of graphite        were used, whilst the mechanical properties are significantly        improved, as compared to foam containing from 5 to 6 wt. % of        graphite without addition of Sidistar T120.

The polymer used in accordance with all aspects of the invention isbased on one (or more) vinyl aromatic monomer(s), preferably styrene,and optionally one or more comonomers, i.e. it is a homopolymer or acopolymer.

The addition to styrene, a co-monomer of a specific styrene comonomerpossessing steric hindrance, in particular p-tert-butylstyrene, oralpha-methyl styrene comonomer, or some other sterically hinderedstyrene comonomer, may advantageously increase the glass transitiontemperature of such a vinyl aromatic copolymer. In such a manner, theaddition of a specific styrene comonomer to the styrene monomer improvesthe thermal stability of vinyl aromatic copolymer, which subsequentlyleads to better dimensional stability of moulded blocks made thereof.

The vinyl aromatic copolymer as used in the present invention ispreferably comprised of 1 to 99 wt. % of styrene monomer andcorrespondingly 99 to 1 wt. % of p-tert-butylstyrene monomer, as follows(amounts in wt. %, based on the total amount of monomer):

Preferred More preferred Most preferred Monomer (wt. %) (wt. %) (wt. %)Styrene 1-99 50-99 70-98 p-tert-Butylstyrene 99-1   1-50 30-2 

Alternatively, the vinyl aromatic copolymer as used in the presentinvention is preferably comprised of 1 to 99 wt. % of styrene monomerand correspondingly 99 to 1 wt. % of alpha-methyl styrene monomer, asfollows (amounts in wt. %, based on the total amount of monomer):

Preferred More preferred Most preferred Monomer (wt. %) (wt. %) (wt. %)Styrene 1-99 50-98 75-95 alpha-methyl 99-1   2-50 25-5  Styrene

In addition to the mandatory components a) and b) above, the materialsaccording to the invention (the polymer composition, the granulate, thefoam and the masterbatch) may contain further additives, as is set outbelow.

For instance, the polymer foam preferably further comprises one or moreathermanous additives selected from a) powder inorganic additive otherthan silica, b) powder carbonaceous additive other than graphite, and c)powder geopolymer or powder geopolymer composite. The powder inorganicadditive is preferably selected from powders of calcium phosphate andmineral with perovskite structure. The powder carbonaceous additive ispreferably selected from powders of carbon black, petroleum coke,graphitized carbon black, graphite oxides and graphene.

Calcium Phosphate

The calcium phosphate as typically used according to the invention has aparticle size, as measured by laser diffraction, of 0.01 μm to 100 μm.It is preferred that the particle size is from 0.1 μm to 50 μm, such as0.5 μm to 30 μm. The calcium phosphate is preferably tricalciumphosphate (specifically a type of hydroxyapatite).

According to the present invention, the calcium phosphate, if present,is preferably used in an amount of from 0.01 to 50 wt. %, based on theweight of vinyl aromatic polymer including solid and, if any, liquidadditives, but exclusive of propellant, more preferably 0.1 to 15 wt. %,most preferably 0.5 to 10 wt. %, in particular 1 to 8 wt. %.

Perovskite

In a preferred embodiment of the present invention, the thermalconductivity (as measured according to ISO 8301) is decreased, themechanical properties are improved (compressive and bending strengthsare increased, as measured according to EN 13163) and/or theself-extinguishing properties are improved (as measured according to ENISO 11925, or even as measured according to DIN 4102/B1, B2) in vinylaromatic polymer foam, by use of a mineral of the general formula ABX₃,A and B being cations and X being anions, wherein the mineral hasperovskite crystal structure (in the following “mineral havingperovskite structure”, or “perovskite”). This type of additive reducesflame development by the creation of char with higher viscosity and thusreduces dripping and flaming.

The preferred concentration of perovskite for a decrease of the thermalconductivity, an additionally increase of self-extinguishing andmechanical properties is in a range of from 0.01 to 50 wt. %, based onthe weight of vinyl aromatic polymer in the granulate including solidand, if any, liquid additives, but exclusive of propellant, morepreferably 0.05 to 25 wt. %, most preferably 0.1 to 15 wt. %, inparticular 0.5 to 12 wt. %, such as 1 to 8 wt. %.

Preferably, A is selected from the group consisting of Ca, Sr, Ba, Bi,Ce, Fe, and mixtures thereof. Moreover, the A atom can be representedalso by hybrid organic-inorganic groups, e.g. (CH₃NH₃)⁺.

The B atom is preferably represented by Ti, Zr, Ni, Al, Ga, In, Bi, Sc,Cr, Pb as well as ammonium groups. The X atom is preferably representedby oxygen or halide ion, or mixtures thereof.

Among the most preferred representatives of perovskite structures aredielectric BaTiO₃, high-temperature semiconductor YBa₂Cu₃O_(7-x),materials exhibiting magneto-resistance R_(1-x)A_(x)MnO₃, where R=La³⁺,Pr³⁺ or other earth ion, A=Ca²⁺, Sr²⁺, Ba²⁺, Bi²⁺, Ce²⁺, andmultiferroic materials.

Perovskites have large reflectance properties in the broad wavelengthand a high optical constant, even in the far-infrared region. Hence,perovskites are infrared reflective materials that reflect infrared raysincluded in sunlight or the like and reduce the amount of absorbedenergy in the infrared range.

A preferred perovskite has a BET surface size in the range of from 0.01to 100 m²/g, as measured according to the standards ASTM C1069 and ISO9277 as explained above. The BET active surface is preferably in a rangeof from 0.05 to 50 m²/g and more preferable in a range of from 0.1 to 15m²/g.

Typical perovskites have an average particle size in a range of from0.01 to 100 μm, as measured according to the standard procedure using aMalvern Mastersizer 2000 apparatus. The average particle size ispreferably in a range of from 0.1 to 50 μm, more preferably in a rangeof from 0.5 to 30 μm.

Geopolymer

It has further been found that it is possible to maintain the foam'sself-extinguishing and mechanical properties in the same range as in anexpanded polymer without addition of filler or any other athermanousadditive, while at the same time the thermal conductivity can bedecreased significantly, namely by addition of a geopolymer, or ageopolymer composite prepared from geopolymer and various types ofathermanous fillers. This is possible because the geopolymer itselfgives fire resistance, and may in the composite encapsulate theparticles of athermanous additive, especially those additives based oncarbon, and separates them from any interactions with the flame, thepolymer or the flame retardant. Geopolymer and geopolymer compositefurther decrease thermal conductivity, based on a heat radiationscattering effect.

Geopolymer synthesis from aluminosilicate materials takes place by theso-called geopolymerization process, which involves polycondensationphenomena of aluminates and silicate groups with formation ofSi—O—Al-type bonds. In a preferred embodiment, geopolymers encapsulatecarbon-based athermanous fillers in a matrix and limit the contact(interphase) between carbon-based filler and brominatedflame-retardants, including those based on polystyrene-butadienerubbers. This phenomenon allows a significant decrease of the requiredconcentration of brominated flame retardant in expandable vinyl aromaticpolymer composites.

A preferred geopolymer composite is prepared by a process wherein anathermanous additive component is present during the production ofgeopolymer composite, so that the geopolymer composite incorporates theathermanous additive component. Preferably, this athermanous additivecomponent comprises one or more athermanous additives selected from thegroup consisting of

-   -   a. carbon black, petroleum coke, graphitized carbon black,        graphite oxides, various types of graphite (especially poor and        amorphous forms with a carbon content in the range of from 50 to        90%) and graphene, and    -   b. titanium oxides, ilmenite, rutiles, chamotte, fly ash, fumed        silica, hydromagnesite/huntite mineral, barium sulfate and        mineral with perovskite structure, preferably the athermanous        additive component comprises one or more carbon-based        athermanous additives selected from the group of heat absorbers        and heat reflectors,    -   in particular the athermanous additive component is carbon        black, graphite, or a mixture thereof.

Further details of the preparation of geopolymer composite may be foundin the international application entitled “Geopolymer and compositethereof and expandable vinyl aromatic polymer granulate and expandedvinyl aromatic polymer foam comprising the same”, PCT/EP2016/050594,filed on even date herewith.

Moreover, further carbon-based athermanous additives (other than thespecific type of graphite) can be present in the foam, such as carbonblack, petroleum coke, graphitized carbon black, graphite oxides, andgraphene.

Carbon Black

The carbon black as preferably used according to the invention has a BETsurface, as measured according to ASTM 6556, of more than 40 to 250m²/g.

It is preferred that the BET surface of the carbon black as usedaccording to the invention is from 41 to 200 m²/g, preferably from 45 to150 m²/g, in particular from 50 to 100 m²/g.

The sulphur content of the carbon black as preferably used according tothe invention is in the range of from 50 to 20,000 ppm, as measuredaccording to ASTM D1619, preferably from 3,000 to 10,000 ppm.

The carbon black is preferably present in an amount of 0.1 to 12 wt. %,based on the weight of the vinyl aromatic polymer including additives,but exclusive of propellant, preferably 0.2 to 12.0 wt. %, morepreferred 0.5 to 9.0 wt. %, such as 1.0 to 8.0 wt. %, in particular 2.0to 7.0 wt. %, such as 3.0 to 6.0 wt. %, e.g. about 5.0 wt. %.

In the following, a) the specific type of silica and b) the specifictype of graphite will be referred to as the mandatory athermanousfillers or additives. The further athermanous fillers that arepreferably present, namely s) one or more of calcium phosphate, mineralwith perovskite structure, and geopolymer and/or geopolymer composite,and t) one or more of carbon black, petroleum coke, graphitized carbonblack, graphite oxides, and graphene, will be referred to as optionalathermanous fillers or additives.

The foam also preferably comprises one or more of nucleating agent,flame retardant, synergist, thermal oxidative stabiliser, flameretardant thermal stabiliser, and dispersion aid.

For instance, the flame retardant system is, especially in an extrusionprocess, usually a combination of two types of compounds, namely x) abrominated aliphatic, cycloaliphatic, aromatic or polymeric compoundcontaining at least 50 wt. % of bromine, and a second compound (socalled synergistic compound, y) which can be bicumyl (i.e.2,3-dimethyl-2,3-diphenylbutane) or 2-hydroperoxy-2-methylpropane, ordicumyl peroxide, cumene hydroxide, or 3,4-dimethyl-3,4-diphenylbutane.

The total content of flame retardant system, i.e. x) plus y), istypically in a range of from 0.1 to 5.0 wt. % based on the weight ofvinyl aromatic polymer including solid and, if any, liquid additives,but exclusive of propellant, preferably between 0.2 and 3 wt. %. Theweight-to-weight ratio of bromine compound x) to synergistic compound y)is preferably in a range of from 1:1 to 15:1, usually in a range of from3:1 to 10:1, in particular from 2:1 to 7:1.

In a further aspect, the invention relates to (II) processes for thepreparation of expandable polymer granulate.

In a first embodiment (IIa), the process is a process for thepreparation of expandable polymer granulates comprising the followingsteps:

i) feeding vinyl aromatic polymer into an extruder,

ii) adding a) the silica and b) the graphite, and optionally thermalstabiliser and flame suppressant,

iii) injecting blowing agent into the melt of polymer,

iv) extruding the homogenous blend, and

v) pelletizing the blend in an underwater pelletizer, so as to obtainthe granulate.

Preferably, the extrusion process (IIa) comprises the steps:

-   -   i) feeding a first polymer component comprising vinyl aromatic        polymer into a first mixer;    -   ii) feeding a first additive component a) into the first mixer,        to produce a first mixture from the first polymer component and        the first additive component;    -   iii) feeding a second polymer component b) comprising vinyl        aromatic polymer into a second mixer;    -   iv) feeding a second additive component b) into the second        mixer, to produce a second mixture from the second polymer        component and the second additive component, wherein the        processing conditions in the second mixer are more severe than        the processing conditions in the first mixer, by providing        higher shear force;    -   v) combining the first and second mixtures, to produce a third        mixture;    -   vi injecting blowing agent c) into the third mixture, to produce        a fourth mixture;    -   vii) mixing the fourth mixture; and    -   viii) pelletizing the fourth mixture, to obtain the granulate.

The first polymer component can be a vinyl aromatic polymer having amelt index from 4 to 20 g/10 min, as measured according to ISO 1133.

The second polymer component can be a vinyl aromatic (e.g. styrene)homopolymer (or preferably copolymer with p-tert butyl styrene oralpha-methyl styrene), having a melt index ranging from 4 to 30 g/10min, as measured according to ISO 1133.

According to this first and preferred embodiment of the second aspect,the invention allows for the separate addition of first and secondadditive components into a mixture that is ultimately charged withpropellant and is pelletized, so as to obtain the expandable granulate.Because of the separate addition of the first and second additivecomponents, the process is highly flexible and allows for the processingof additives that have very different processing requirements, inparticular in view of their stability under those processing conditionsthat are necessary so that the different additive components can bestperform their desired function. Typically, at least a part (andpreferably all) of the a) silica and/or b) graphite as defined above isintroduced as part of the second additive component in this extrusionprocess, whereas at least a part (and preferably all) of the flameretardant system is introduced as part of the first additive componentin this extrusion process. This is advantageous since the flameretardant system typically requires more moderate processing conditions,in particular as compared to a) silica and b) graphite. Thus, accordingto the invention, a mixture comprising a) silica and b) graphite can beprepared in a dedicated mixer that provides for the high shearing thatis preferred for these types of additives, so that they are properlydispersed.

As a first alternative, the second additive components (e.g. themandatory and optional athermanous fillers) can be mixed with polymer,in equipment that provides for high shearing and good dispersion, andthe obtained mixture is directly, i.e. as a melt, combined with themixture containing the first additive components, to give a mixture thatis ultimately charged with blowing agent.

As a second alternative, the second additive components (e.g. themandatory and optional athermanous fillers) can be mixed with polymerand be provided as a masterbatch. Such a masterbatch is advantageous incase the plant design does not allow for the processing conditions thatare preferable for the a) silica and/or b) graphite, e.g. high shearingconditions. The masterbatch can for instance be prepared off-site, indedicated processing equipment, and having to provide such processingequipment on site can be dispensed with. The masterbatch comprising themandatory and optional athermanous fillers is subject of the fifthaspect of the present invention, and is described below.

According to a second embodiment of the second aspect (IIb), expandablepolymer granulates is prepared in an aqueous suspension polymerizationprocess comprising the steps:

-   i) adding a vinyl aromatic monomer and optionally one or more)    comonomers to the reactor, and subsequently adding    -   i1) optional polymeric suspension aid,    -   i2) athermanous fillers (mandatory and optional ones),    -   i3) flame retardant,    -   i4) at least one peroxide (or the mixture of two or more        peroxides) as reaction initiator,-   ii) adding the demineralised water, and    -   ii1) at least one suspending agent which is an inorganic acid        salt,    -   ii2) at least one peroxide (or the mixture of two or more        peroxides) as reaction initiator,    -   ii3) at least one suspension stabilizer selected from the group        of anionic surface active compounds and/or high molecular weight        compounds (e.g. hydrophilic and/or amphiphilic polymers), and-   iii) continuing the polymerization (preferably until the    concentration of vinyl aromatic monomer(s) is below 1000 ppm by    weight, based on the weight of the polymer),-   iv) adding the blowing agent during or after the polymerization    step,-   v) cooling, and then separating the granulate from the water.

The athermanous fillers that are mandatory according to the presentinvention (namely a) silica, and b) graphite) may be added in the formof a masterbatch, they may be introduced at the beginning of thesuspension polymerization process, or may be dissolved in the monomerand/or a mixture of the monomer and comonomer. The same applies for theoptional athermanous fillers, s) and t) as mentioned above.

According to the present invention, the mandatory and the optionalathermanous fillers are introduced as athermanous fillers i2), and theymay also be introduced in step ii) and/or in step iii) of thissuspension process.

The polymer granulate is prepared using well known inorganic salts ofphosphoric acid, such as types of calcium phosphate, magnesiumphosphate, or a combination of salts as suspending agents. These saltsmay be added to the reaction mixture in a finely divided form, or as aproduct of an in situ reaction (for example, between sodium phosphateand magnesium sulphate).

The salts are supported in their suspending action by anionicsurface-active compounds, such as sodium dodecylobenzene sulfonate orsodium poly(naphthalene formaldehyde) sulfonate. Those surface-activecompounds can be also being prepared in situ using their precursors suchas sodium metabisulfite and potassium persulfate. The suspension can bealso stabilized by high molecular weight organic polymers, such aspolyvinyl alcohol or hydroxyethylcellulose orhydroxypropylmethyl-cellulose.

To improve the stability of the suspension, up to 30 wt. % of polymer(fresh vinyl aromatic polymer or waste vinyl aromatic polymer from aprevious polymerization) may be added as the optional suspension aid,preferably 5 to 15 wt. %, based on the vinyl aromatic monomer amount. Itincreases the viscosity of the reagent mixture (monomer with alladditives), which facilitates the creation of a suspension. The same orsimilar effect can be achieved by mass pre-polymerization of the monomeror mixture of comonomers and additives until the suitable melt viscosityis obtained (as for 1% to 30% of polymer concentration).

In the most preferred process, before start of the polymerization stepiii), athermanous fillers in the form of a concentrated masterbatch areadded to the styrene and/or its mixture with comonomer, particularlyp-tert-butylstyrene. The masterbatch can contain from 10 to 60% ofathermanous fillers, the mandatory ones, a) and b), and the optionalones, s) and t), pre-silanized or silanized in the masterbatchcompounding process by e.g. triethoxy(phenyl)silane, to decrease itshydrophilic properties.

The polymerization is then continued in an aqueous suspension phase, inthe presence of the above-mentioned suspending agents, suspensionstabilizers, athermanous fillers, flame retardants and suppressors,optionally at least in the presence of suspension aid.

The polymerization process is triggered by initiators. Normally, twoorganic peroxides are used as initiators. The first peroxide, with ahalf-life of about one hour at 80-95° C., is used to start and run thereaction. The other, with a half-life of about one hour at 105-125° C.,is used during the following polymerization process continued in thehigher temperature, so called high temperature cycle (HTC). For abovespecific process with the presence of carbon black was used compositionof three peroxides to achieve suitable average molecular weight despitenegative inhibiting effect caused by the carbon black presence.Preferably were used: dicumyl peroxide and tert-butylperoxy-2-ethylhexyl carbonate peroxide as high temperature cycle peroxides (120° C.)and tert-butyl 2-ethylperoxyhexanoate as low temperature cycle peroxide(82-90° C.)

The end of the process is typically indicated by a concentration ofresidual vinyl monomer(s) of below 1000 ppm by weight, based on the massof vinyl aromatic polymer or copolymer. The vinyl aromatic polymer orcopolymer which is obtained at the end of the process typically has anaverage molecular mass (Mw) ranging from 50 to 600 kg/mol, preferablyfrom 150 to 450, most preferably from 100 to 350 kg/mol. The procedurefor controlling molecular mass in suspension polymerization is wellknown and is described in detail in Journal of Macromolecular Science,Review in Macromolecular Chemistry and Physics C31 (263) p. 215-299(1991).

During the polymerization process, conventional additives can be addeddirectly to the monomer(s), their solution with suspension aid, to thepre-polymer, or to the suspension. Additives such as the flame retardantsystem, nucleating agents, antistatic agents, blowing agents andcolorants stay in the polymer drops during the process and are thuspresent in the final product. The concentrations of conventionaladditives are the same as for the extrusion process, as set out above.

The flame retardant systems suitable for the present suspension processare similar to those used in the extrusion process described above. Onesuitable system is the combination of two types of compounds, namely abrominated aliphatic, cycloaliphatic, aromatic or polymeric compoundcontaining at least 50 wt. % of bromine (such ashexabromo-cyclododecane, pentabromomonochlorocyclohexane, or a polymericbromine compound, specifically brominated styrene-butadiene rubber) anda second compound called synergistic compound which can be e.g. aninitiator or peroxide (dicumyl peroxide, cumene hydroxide, and3,4-dimethyl-3,4-diphenylbutane). The content of flame retardant systemis typically in a range of from 0.1 to 5.0 wt. % with respect to thetotal weight of vinyl aromatic polymer (weight of monomer(s) plus weightof polymer if added on the start), preferably between 0.2 and 3 wt. %.The ratio between bromine compound and synergistic compound ispreferably in a range of from 1:1 to 15:1 weight to weight, usually from3:1 to 5:1.

The blowing agent or agents are preferably added during thepolymerization to the suspension phase and are selected from aliphaticor cyclic hydrocarbons containing from 1 to 6 carbons and theirderivatives. Typically are used n-pentane, cyclopentane, i-pentane,combination of two of them or their mixture. In addition, thehalogenated aliphatic hydrocarbons or alcohols containing from 1 to 3carbons are commonly used. The blowing agent or agents can also be addedafter the end of polymerization.

At the end of the polymerization, spherical particles of expandablestyrenic polymer are obtained as granulate, with an average diameterrange of 0.3 to 2.3 mm, preferably from 0.8 to 1.6 mm. The particles canhave different average molecular mass distribution, depending on theirsize, but all contain used additives dispersed homogenously in thepolymer matrix.

In the final step after the HTC step, the mass is cooled down to e.g.35° C., and the polymer granulate is separated from the water,preferably in a centrifuging process. The particles are then dried andpreferably coated with a mixture of mono- and triglycerides of fattyacids and stearic acid salts.

After discharging the particles from the reactor, they are typicallywashed: first with water, then with non-ionic surfactant in aqueoussolution, and finally again with water; they are then desiccated anddried with hot air having a temperature in the range 35-65° C.

The final product is typically pre-treated by applying a coating (thesame as for the extruded granulate) and can be expanded by the samemethod as the extrusion product.

According to a third embodiment of the second aspect (IIc), expandablepolymer granulate is prepared in a continuous mass process comprisingthe following steps:

i) providing continuously to a mass prepolymerization reactor (or thefirst from a cascade reactor) a stream of:

-   -   i1) vinyl aromatic monomer and optionally at least one comonomer        (preferably p-tert-butylstyrene),    -   i2) at least one additive solution, and    -   i3) optionally recycled monomer,

ii) continuing polymerization in the prepolymerization reactor or thesequence of cascade reactors,

iii) adding athermanous fillers (mandatory and optional ones),

iv) degassing the polymer,

v) feeding the polymer in molten state into the extruder, preferablydirectly from the polymerization plant,

vi) optionally adding a flame retardant system including synergist andthermal stabilisers,

vii) injecting the blowing agent,

viii) extruding the homogenous polymer mixture, and

ix) pelletizing in an underwater pelletizer, so as to obtain thegranulate.

The reactor or cascade reactor is preferably arranged horizontally. If acascade reactor is used, then there are preferably up to 5 reactors, inparticular up to 4, such as three reactors.

The continuous mass polymerization is process congruous to the extrusionprocess, but the vinyl aromatic polymer or copolymer together withathermanous fillers is used in a molten state and the extruder is feddirectly by the polymerization plant.

The mass polymerization reactor (or first from cascade reactors) is fedcontinuously by vinyl aromatic monomer, particularly styrene, andoptionally by its vinyl aromatic comonomer, for instancep-tert-butylstyrene.

At this stage, athermanous fillers in the form of a masterbatch or inthe form of powders are fed into the mass polymerisation reactor, one ormore additives and optionally recycled monomer recovered from theprocess.

The athermanous additives (e.g. masterbatches) are preferably dissolvedin the vinyl aromatic monomer or before feed to the polymerizationreactor.

The polymerisation reaction is initiated thermally, without addition ofinitiators. In order to facilitate heat collection, polymerisation isgenerally carried out in the presence of for instance monocyclicaromatic hydrocarbon.

The prepolymerised mass from the pre-polymerisation reactor is pumpedthrough the sequence of several horizontal reactors, and thepolymerisation reaction is subsequently continued.

At the end of the mass polymerization stage, the rest of unpolymerizedmonomer is removed by degassing of the melt.

A vinyl polymer in the molten state, produced in mass polymerization andcontaining athermanous fillers, is fed into an extruder at a temperaturein a range of from 100 to 250° C., preferably from 150 to 230° C. In thenext stage, the flame retardant system and the nucleating agent are fedto the polymer melt. Again, a combination of two types of flameretarding compounds can be used, namely a brominated aliphatic,cycloaliphatic, aromatic or polymeric compound containing at least 50wt. % of bromine, and a second compound called synergistic compound,which can be bicumyl (2,3-dimethyl-2,3-diphenylbutane) or2-hydroperoxy-2-methylpropane. The concentrations of additives aretypically the same as for the extrusion process, as set out above.

In the following step, the blowing agent is injected into the moltenpolymer mixture and mixed. The blowing agent or agents are the same asfor the suspension process, i.e. selected from aliphatic or cyclichydrocarbons containing from 1 to 6 carbons and their derivatives. Thepolymer with all additives and blowing agent is subsequently extruded togive expandable beads.

The homogenous polymer mixture comprising additives and blowing agent ispumped to the die, where it is extruded through a number of cylindricaldie holes with 0.5-0.8 mm of diameter, immediately cooled by a waterstream and cut with a set of rotating knives in a pressurized underwaterpelletizer, to obtain micropellets (granulate).

The micropellets are transported by water, washed, drained off andfractioned. The final product is pre-treated in the same way as it is inthe suspension and extrusion processes.

In a further aspect, the invention relates to (III) expandable polymergranulate comprising one or more propellants, a) the silica, b) thegraphite and c) vinyl aromatic polymer, wherein the silica and thegraphite are present in a weight ratio in a range of from 1:1 to 1:10.

Preferably, the expandable polymer granulate is obtainable (and is morepreferably obtained) by the process according to the second aspect.

Preferably, the expandable polymer granulate further comprises one ormore of the optional athermanous additives s) and t) above, morepreferably the expandable polymer granulate further comprises one ormore additives selected from s) powders of calcium phosphate, mineralwith perovskite structure, geopolymer and geopolymer composite, and t)carbon black, petroleum coke, graphitized carbon black, graphite oxides,and graphene.

In a further aspect, the invention relates to (IV) expanded polymer foamcomprising a) silica, b) graphite and c) vinyl aromatic polymer, whereinthe silica and the graphite are present in a weight ratio in a range offrom 1:1 to 1:10, the foam having

-   -   a density of 8 to 30 kg/m³, and    -   a thermal conductivity of 25-35 mW/K·m.

The expanded polymer foam is preferably obtainable (and is mostpreferably obtained) by expansion of the expandable polymer granulateaccording to the third aspect.

According to the fifth aspect, the invention relates to (V) amasterbatch. The masterbatch comprises a) the specific silica, b) thespecific graphite, and c) vinyl aromatic polymer, and the total amountof a) and b) (i.e. the sum of the amounts of a) the silica and b) thegraphite, respectively) is in a range of from 10 to 70 wt. %, based onthe weight of the masterbatch.

In a general embodiment, a) the silica and b) the graphite need notnecessarily be present in the masterbatch in a weight ratio in a rangeof from 1:1 to 1:10, as part of a) the silica and/or b) the graphite maybe introduced into the process by other means, i.e. without beingpresent in the masterbatch.

However, in a preferred embodiment, a) the silica and b) the graphiteare present in the masterbatch in a weight ratio in a range of from 1:1to 1:10. This will provide the advantageous mandatory additives in theadvantageous ratio to the process (II). More preferably, a) the silicaand b) the graphite are used in a weight ratio a):b) in a range of from1:1.5 to 1:8, most preferably a) the silica and b) the graphite are usedin a weight ratio a):b) in a range of from 1:2 to 1:5, in particular a)the silica and b) the graphite are used in a weight ratio a):b) of about1:3.

Preferably, the total amount of a) and b) is in a range of from 10 to 65wt. %, based on the weight of the masterbatch, more preferably from 20to 60 wt. %, in particular from 25 to 55 wt. %.

In a preferred embodiment, c) is a vinyl aromatic polymer having a meltindex in a range of from 4 to 30 g/10 min, as measured according to ISO1133, and the vinyl aromatic polymer is preferably a homopolymer orcopolymer with p-tert butyl styrene or alpha-methyl styrene.

The masterbatch may, in addition to the mandatory components a) silica,b) graphite, and c) vinyl aromatic polymer, comprise further components,such as one or more of the optional athermanous additives s) and t).Preferred optional athermanous fillers that are preferably present inthe masterbatch are s) one or more of calcium phosphate, mineral withperovskite structure, and geopolymer and/or geopolymer composite, and t)one or more of carbon black, petroleum coke, graphitized carbon black,graphite oxides, and graphene. These optional athermanous fillers veryoften require processing conditions that are similar to silica andgraphite.

Moreover, the masterbatch preferably comprises one or more silanes.Preferred silanes are for example aminopropyltriethoxysilane (e.g.Dynasylan AMEO from Evonik), aminopropyltrimethoxysilane (e.g. DynasylanAMMO from Evonik), and phenyltriethoxysilane (e.g. Dynasylan 9265 fromEvonik).

Preferably, the amount of silane is in a range of from 0.01 to 1 wt. %,based on the weight of the athermanous additive in the masterbatch.

It is noted that, unlike the properties of the additives as startingmaterials, the properties of additives as contained in granulate or foamare notoriously difficult to determine.

It is often considered more appropriate in the art to characterize theadditives in granulate and foam with reference to the properties of theadditives as initially used.

The advantages of the present invention become apparent from thefollowing examples. Unless indicated otherwise, all percentages aregiven by weight.

Moreover, whenever reference is made in the present description of theinvention to an amount of additive “by weight of vinyl aromaticpolymer”, this refers to the amount of the additive by weight of polymercomponent inclusive of (solid and, if any, liquid) additives, butexclusive of propellant.

EXAMPLES

In Accordance with the Invention, Expandable Polymer Granulate wasPrepared in an Extrusion Process, with Addition of Athermanous Fillersin Powder Form (Examples 1 to 8):

Example 1 (Comparative)

A mixture of vinyl aromatic polymer in the form of granules, containing2.0 wt. % of polymeric brominated flame retardant (Emerald 3000), 0.4wt. % of bicumyl, Irganox 1010 in an amount of 0.1 wt. %, Irgafos 126 inan amount of 0.1 wt. % and Epon 164 in an amount of 0.2 wt. % were dosedto the main hopper of the main 32D/40 mm twin-screw co-rotatingextruder. The melt temperature in the main extruder was 180° C.

The graphite powder (CR CR5995 from company GK) in an amount of 3 wt. %,based on total weight of granulate, excluding propellant, was dosed tothe side arm (54D/25 mm) twin-screw co-rotating extruder via one sidefeeder and the vinyl aromatic polymer (in the form of granules) wasdosed to the main hopper of this extruder. The melt containing 30 wt. %of concentrated graphite was transported to the main extruder. The melttemperature inside the extruder was 190° C.

The blowing agent (n-pentane/isopentane mixture 80/20%) was injected tothe main 32D/40 mm extruder downstream from the injection of the meltfrom the side twin-screw extruder. The concentration of blowing agentwas 5.5 wt. %, calculated on total mass of product.

The melt of vinyl aromatic polymer containing flame retardant, bicumyl,graphite and blowing agent was transported to the 30D/90 mm coolingextruder and pumped through a 60 mm length static mixer, melt pump,screen changer, diverter valve and extruded through the die head with0.75 mm diameter holes, and underwater pelletized by the rotatingknifes. Downstream, the rounded product, a granulate with a particlesize distribution of 99.9% of the fraction 0.8-1.6 mm was centrifuged toremove the water, and was finally coated with a mixture of magnesiumstearate with glycerine monostearate and tristearate. The melttemperature in the cooling extruder was 170° C.

The coated beads were expanded to measure the final general propertiesof expanded foam composite:

-   -   thermal conductivity according to standard ISO 8301.    -   mechanical properties (compressive and bending strength)        according to standard EN 13163.    -   flammability according to tests methods: EN ISO 11925-2 and DIN        4102 B1, B2.

Example 2 (According to the Invention)

The components according to Example 1 were used. Additionally, aspherically-shaped amorphous silicon dioxide from ELKEM (Sidistar T120as specified above) in an amount of 1 wt. % was used. The silica powderwas initially mixed together with the graphite powder and the mixturewas then dosed to the side arm (54D/25 mm) twin-screw co-rotatingextruder via one side feeder. The melt in the side extruder was in thatcase 40 wt. % concentrated.

Example 3 (Comparative)

The components according to Example 1 were used. Graphite (CR5995) in anamount of 4 wt. % was used.

Example 4 (According to the Invention)

The components according to Example 3 were dosed and thespherically-shaped amorphous silicon dioxide from ELKEM (Sidistar T120as specified above) was added in an amount of 1.3 wt. %. The melt inside extruder was in that case 40 wt. % concentrated.

Example 5 (Comparative)

The components according to Example 1 were dosed. The graphite (CR5995)content was increased to 5 wt. %. This example was performed especiallyto show that better foam properties are actually obtained in Examples 2and 4 where the graphite content was lower and Sidistar silica was used.

Example 6 (Comparative)

The components according to Example 1 were used. Irganox 1010, Irgafos126 and Epon 164 were not added.

Example 7 (According to the Invention)

The components according to Example 2 were used. Irganox 1010, Irgafos126 and Epon 164 were not added.

Example 8 (According to the Invention)

The components according to Example 4 were used. Irganox 1010, Irgafos126 and Epon 164 were not added.

TABLE 1 Summary of Examples 1 to 8. Components Examples (wt. %) 1* 2 3*4 5* 6* 7 8 GP585X + + + + + + + + Graphite GK 3 3 4 4 5 3 3 4 CR5995Sidistar T120 — 1 — 1.3 — — 1 1.3 Emerald 3000 2.0 2.0 2.0 2.0 2.0 2.02.0 2.0 Bicumyl 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Irganox 1010 0.1 0.1 0.10.1 0.1 — — — Irgafos 126 0.1 0.1 0.1 0.1 0.1 — — — Epon 164 0.2 0.2 0.20.2 0.2 — — — Polywax 2000 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Pentane/Iso-5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 pentane 80/20 *Comparative Example

TABLE 2 Examples 1 to 8. Final product parameters at a foam density ofca. 19.0 g/l. Examples 1* 2 3* 4 5* 6* 7 8 Thermal 30.8 30.2 30.4 29.730.1 31.0 30.4 29.0 conductivity (mW/m · K)/ISO 8301/Flammability/ + + + + + + + + EN ISO 11925-2/ Flammability/ +/+ +/+ +/++/+ +/+ +/+ +/+ +/+ DIN 4102 B1/B2/ Compressive 106 118 98 117 94 98 120118 strength at 10% def. (kPa)/EN 13163/ Bending strength 170 196 166202 160 169 200 201 (kPa)/EN 13163/ Passed (+ or B2 or B1); Not passed(−) *Comparative Example

Expandable Polymer Granulate was Further Prepared in an ExtrusionProcess, However with Addition of Athermanous Fillers in the Form of aMasterbatch (Examples 9 to 13):

Examples from 1 to 5 were repeated, with the difference that the mixtureof graphite with silica was added to the main co-rotating twin-screwextruder in the form of a 40 wt. % concentrated masterbatch. In theexample where graphite was used without silica, the masterbatchconcentration was 30 wt. %. The masterbatches were prepared on the sameextruder as the side arm co-rotating twin-screw extruder—54D/25 mm.Synthos PS 585X was used as masterbatch polymer carrier. The results arevery similar to those obtained for Examples 1 to 5 above.

Expandable Polymer Granulate was Prepared in a Suspension Process(Examples 14 to 18):

Example 14 (According to the Invention)

20 000 kg of styrene were dosed to a 60 m³ reactor. The followingcomponents (calculated per weight of styrene) were then added: 4.0 wt. %of athermanous fillers silanized with 0.1 wt. % of silane—Dynasylan 9265(including 3.0 wt. % of graphite CR5995 from company GK and 1.0 wt. % ofsilica Sidistar T120 from Elkem company) in the form of a 40 wt. %concentrated masterbatch based on Synthos PS 585X, 0.002 wt. % ofdivinylbenzene, 1 wt. % of Emerald 3000, 0.3 wt. % of Polywax 1000, and0.5 wt. % of dicumyl peroxide.

The mixture was heated relatively quickly to a temperature of 70° C. andmixed at this temperature for 30 min with 275 rpm. Then, the temperaturewas increased to 90° C. and 30 000 kg of demineralised water(temperature of 60° C.) were added. The mixing force immediately createda suspension of prepolymer and the suspension was heated to 82° C.Immediately, 0.3 wt. % of Peroxan PO and 0.5 wt. % of TBPEHC were added.The radical polymerization was started and the following surfactantcomposition was introduced:

-   -   potassium persulfate—0.0001 wt. %    -   Poval 205-0.18 wt. % of 5% concentrated water solution    -   Poval 217 (alternatively Poval 224)—0.09 wt. % of a 5        concentrated water solution    -   DCloud 45-0.1 wt. %    -   Arbocel CE 2910HE50LV—0.1 wt. % (hydroxypropylmethyl-cellulose        supplied by J. RETTENMAIER & SOHNE GMBH)

The polymerization was then continued for 120 min. at a temperature of82° C., and the temperature was then increased to 90° C. The suspensionwas kept at this temperature for 120 min. to achieve particle identitypoint of suspension. A further portion of Poval 217 (in a concentrationof 0.3 wt. % of a 5 wt. % concentrated solution in water) wasintroduced. In this step, sodium chloride can be added in an amount of0.5 wt. % per water phase, to reduce the water content in the polymer.Alternatively, a surfactant (sodium dodecylbenzenesulfonate, SDBS) canbe used in an amount of 0.2 wt. %.

The reactor was closed and the n-pentane/isopentane 80/20% mixture in anamount of 5.5 wt. % was added over 60 min. Simultaneously, thetemperature was increased to 125° C. Then the polymerization wascontinued for 120 min. and after that time the suspension slurry wascooled down to 25° C.

The product was removed from the reactor and water was removed in abasket centrifuge. The particles were then dried in a fluid bed drier ata temperature of 40° C. for 30 min. and fractionated on 80% of particlesfraction 0.8-1.6 mm, 15% of 0.3-1.3, 4% of 1.0-2.5 mm and 1% of upperand lower size. Fractions were then coated the same way as the productas obtained in the extrusion process, and then expanded to foam at 35°C. Then the polymer was centrifuged from water and dried in the fluidbed dryer. Finally, after sieving, the granulate was coated with amixture of glycerol monostearate and glycerol tristearate.

Example 15 (According to the Invention)

This example is equivalent to Example 14 but the graphite (CR5995) wasused in an amount of 4 wt. %, and silica (Sidistar T120) in an amount of1.3 wt. %

Example 16 (Comparative)

This example was made according to Example 14; the silica was not used,and graphite was used in an amount of 3 wt. %.

Example 17 (Comparative)

This example was made according to Example 14; the silica was not used,and graphite was used in an amount of 4 wt. %.

Example 18 (Comparative)

This example was made according to Example 14; the silica was not used,and graphite was used in an amount of 5 wt. %.

TABLE 3 Summary of Examples 14 to 18. Components Examples (wt. %) 14 1516** 17** 18** Graphite GK 3 4 3 4 5 CR5995* Sidistar T120* 1 1.3 — — —Emerald 3000 1.0 1.0 1.0 1.0 1.0 *silanized with 0.1 wt. % of Dynasylan9265 **Comparative Example

TABLE 4 Examples 14 to 18. Final product parameters at a foam density ofca. 19.0 g/l. Examples 14 15 16* 17* 18* Thermal conductivity 30.1 29.530.7 30.2 29.8 (mW/m · K)/ISO 8301 Flammability/EN ISO + + + + +11925-2/ Flammability/DIN +/+ +/+ +/+ +/+ −/+ 4102 B1/B2/ Compressivestrength at 110 107 99 95 91 10% def. (kPa)/EN 13163/ Bending strength185 179 170 168 160 (kPa)/EN 13163/ Passed (+ or B2 or B1); Not passed(−) *Comparative Example

Expandable Polymer Granulate was Prepared in a Continuous MassPolymerization Process (Examples 19 to 24):

Example 19 (According to the Invention)

Continuous mass polymerization was carried out in three reactors incascade. The polymerization of styrene was initiated by heating. Thepowder forms of graphite (CR5995) and silica (Sidistar T120), bothsilanized with 0.1 wt. % of silane—Dynasylan 9265, were added to thefirst reactor in a total amount of 4 wt. % (3 wt. % of graphite and 1wt. % of silica). After polymerization and degassing of the polymermelt, the flame retardant was added in a concentration of 1.5 wt. %,together with: bicumyl in a concentration of 0.3 wt. %, Irganox 1010 inan amount of 0.075 wt. %, Irgafos 126 in an amount of 0.075 wt. %, Epon164 in an amount of 0.15 wt. % and nucleating agent—Polywax 2000 in aconcentration of 0.3 wt. %, directly to the extruding raw polystyrene.An extrusion was performed in similar like extruder 32D/40 mm attachedto the degassing unit. During the process, pentane in admixture withisopentane (80/20%) in a concentration of 5.5 wt. % was dosed into theextruder. The granulate form was obtained by means of underwaterpelletizing.

Example 20 (According to the Invention)

This example is equivalent to Example 19, but the graphite (CR5995) wasused in an amount of 4 wt. %, and the silica (Sidistar T120) in anamount of 1.3 wt. %

Example 21 (Comparative)

This example was made according to Example 19; the silica was not used,and graphite was used in an amount of 3 wt. %.

Example 22 (Comparative)

This example was made according to Example 19; the silica was not used,and graphite was used in an amount of 4 wt. %.

Example 23 (Comparative)

This example was made according to Example 19; the silica was not used,and graphite was used in an amount of 5 wt. %.

Example 24 (According to the Invention)

This example was made according to Example 19, but Irganox 1010, Irgafos126 and Epon 164 were not added.

TABLE 5 Summary of Examples 19 to 24. Components Examples (wt. %) 19 2021** 22** 23** 24 GP585X + + + + + + Graphite GK 3 4 3 4 5 3 CR5995*Sidistar 1 1.3 — — — 1 T120* Emerald 3000 1.5 1.5 1.5 1.5 1.5 1.5Bicumyl 0.3 0.3 0.3 0.3 0.3 0.3 Irganox 1010 0.075 0.075 0.075 0.0750.075 — Irgafos 126 0.075 0.075 0.075 0.075 0.075 — Epon 164 0.150 0.1500.150 0.150 0.150 — Polywax 2000 0.3 0.3 0.3 0.3 0.3 0.3 Pentane/ 5.55.5 5.5 5.5 5.5 5.5 Isopentane 80/20 *silanized with 0.1 wt. % ofDynasylan 9265 **Comparative Example

TABLE 6 Examples 19 to 24. Final product parameters at a foam density ofca. 19.0 g/l. Examples 19 20 21* 22* 23* 24 Thermal 30.3 29.9 31.1 30.530.1 30.2 conductivity (mW/m · K)/ISO 8301 Flammability/ + + + + + + ENISO 11925-2/ Flammability/ +/+ +/+ +/+ +/+ −/+ −/+ DIN 4102 B1/B2/Compressive 116 115 106 98 90 114 strength at 10% def. (kPa)/EN 13163/Bending strength 198 200 172 167 162 194 (kPa)/EN 13163/ Passed (+ or B2or B1); Not passed (−) *Comparative Example

The examples show that the foams as prepared according to the inventionnot only have low thermal conductivity, but they also have goodmechanical and self-extinguishing properties.

The invention claimed is:
 1. Expandable polymer granulate comprising oneor more propellants, a) silica, b) graphite and c) polystyrenehomopolymer or copolymer, wherein a) the silica is amorphous and has aBET surface of from 1 to 100 m²/g, an average particle size in a rangeof from 3 nm to 1,000 nm, and the silica is present in an amount of from0.01 to less than 2 wt. %, based on the weight of the polymer (inclusiveof solid and, if any, liquid additives, but exclusive of propellant),and b) the graphite has a carbon content in a range of from 50 to 99.99wt. % and a particle size in a range of from 0.01 to 100 μm, and thegraphite is present in an amount in a range of from 0.01 to 10 wt. %,based on the weight of the polystyrene homopolymer or copolymer(inclusive of solid and, if any, liquid additives, but exclusive ofpropellant) wherein the silica and the graphite are present in a weightratio in a range of from 1:1.5 to 1:10.
 2. The expandable polymergranulate of claim 1, wherein the granulate is obtainable by a processcomprising the following steps: i) providing continuously to a massprepolymerization reactor (or the first from a cascade of reactors) astream of: i1) polystyrene homopolymer or copolymer and optionally atleast one comonomer, i2) at least one additive solution, and i3)optionally recycled monomer, ii) continuing polymerization in theprepolymerization reactor or the sequence of cascade reactors, iii)addition of athermanous fillers: a) silica and b) graphite, andoptionally further additives, iv) degassing the polymer, v) feeding thepolymer in molten state into the extruder, vi) optionally adding a flameretardant system including synergist and thermal stabilisers, vii)injecting blowing agent, viii) extruding the homogenous polymer blend,and ix) pelletizing in an underwater pelletizer, so as to obtain thegranulate, wherein a) the silica is amorphous and has a BET surface offrom 1 to 100 m²/g, an average particle size in a range of from 3 nm to1,000 nm, and the silica is present in an amount of from 0.01 to lessthan 2 wt. %, based on the weight of the polymer (inclusive of solidand, if any, liquid additives, but exclusive of propellant), and b) thegraphite has a carbon content in a range of from 50 to 99.99 wt. % and aparticle size in a range of from 0.01 to 100 μm, and the graphite ispresent in an amount in a range of from 0.01 to 10 wt. %, based on theweight of the polystyrene homopolymer or copolymer (inclusive of solidand, if any, liquid additives, but exclusive of propellant); wherein thesilica and the graphite are used in a weight ratio in a range of from1:1.5 to 1:10.
 3. The expandable polymer granulate of claim 1, whereinthe granulate is obtainable by a process comprising the following steps:i) providing continuously to a mass prepolymerization reactor (or thefirst from a cascade of reactors) a stream of: i1) polystyrenehomopolymer or copolymer and optionally at least one comonomercomprising p-tert-butylstyrene, i2) at least one additive solution, andi3) optionally recycled monomer, ii) continuing polymerization in theprepolymerization reactor or the sequence of cascade reactors, iii)addition of athermanous fillers: a) silica and b) graphite, andoptionally further additives, iv) degassing the polymer, v) feeding thepolymer in molten state into the extruder, vi) optionally adding a flameretardant system including synergist and thermal stabilisers, vii)injecting blowing agent, viii) extruding the homogenous polymer blend,and ix) pelletizing in an underwater pelletizer, so as to obtain thegranulate, wherein a) the silica is amorphous and has a BET surface offrom 1 to 100 m²/g, an average particle size in a range of from 3 nm to1,000 nm, and the silica is present in an amount of from 0.01 to lessthan 2 wt. %, based on the weight of the polymer (inclusive of solidand, if any, liquid additives, but exclusive of propellant), and b) thegraphite has a carbon content in a range of from 50 to 99.99 wt. % and aparticle size in a range of from 0.01 to 100 μm, and the graphite ispresent in an amount in a range of from 0.01 to 10 wt. %, based on theweight of the polystyrene homopolymer or copolymer (inclusive of solidand, if any, liquid additives, but exclusive of propellant); wherein thesilica and the graphite are used in a weight ratio in a range of from1:1.5 to 1:10.
 4. The expandable polymer granulate of claim 1, whereinthe granulate is obtainable by a process comprising the following steps:i) providing continuously to a mass prepolymerization reactor (or thefirst from a cascade of reactors) a stream of: i1) polystyrenehomopolymer or copolymer and optionally at least one comonomer, i2) atleast one additive solution, and i3) optionally recycled monomer, ii)continuing polymerization in the prepolymerization reactor or thesequence of cascade reactors, iii) addition of athermanous fillers: a)silica and b) graphite, and optionally a flame suppressant, iv)degassing the polymer, v) feeding the polymer in molten state into theextruder, vi) optionally adding a flame retardant system includingsynergist and thermal stabilisers, vii) injecting blowing agent, viii)extruding the homogenous polymer blend, and ix) pelletizing in anunderwater pelletizer, so as to obtain the granulate, wherein a) thesilica is amorphous and has a BET surface of from 1 to 100 m²/g, anaverage particle size in a range of from 3 nm to 1,000 nm, and thesilica is present in an amount of from 0.01 to less than 2 wt. %, basedon the weight of the polymer (inclusive of solid and, if any, liquidadditives, but exclusive of propellant), and b) the graphite has acarbon content in a range of from 50 to 99.99 wt. % and a particle sizein a range of from 0.01 to 100 μm, and the graphite is present in anamount in a range of from 0.01 to 10 wt. %, based on the weight of thepolystyrene homopolymer or copolymer (inclusive of solid and, if any,liquid additives, but exclusive of propellant); wherein the silica andthe graphite are used in a weight ratio in a range of from 1:1.5 to1:10.
 5. The expandable polymer granulate of claim 1, wherein thegranulate is obtainable by a process comprising the following steps: i)providing continuously to a mass prepolymerization reactor (or the firstfrom a cascade of reactors) a stream of: i1) polystyrene homopolymer orcopolymer and optionally at least one comonomer, i2) at least oneadditive solution, and i3) optionally recycled monomer, ii) continuingpolymerization in the prepolymerization reactor or the sequence ofcascade reactors, iii) addition of athermanous fillers: a) silica and b)graphite, and optionally further additives, iv) degassing the polymer,v) feeding the polymer in molten state into the extruder directly fromthe polymerization plant, vi) optionally adding a flame retardant systemincluding synergist and thermal stabilisers, vii) injecting blowingagent, viii) extruding the homogenous polymer blend, and ix) pelletizingin an underwater pelletizer, so as to obtain the granulate, wherein a)the silica is amorphous and has a BET surface of from 1 to 100 m²/g, anaverage particle size in a range of from 3 nm to 1,000 nm, and thesilica is present in an amount of from 0.01 to less than 2 wt. %, basedon the weight of the polymer (inclusive of solid and, if any, liquidadditives, but exclusive of propellant), and b) the graphite has acarbon content in a range of from 50 to 99.99 wt. % and a particle sizein a range of from 0.01 to 100 μm, and the graphite is present in anamount in a range of from 0.01 to 10 wt. %, based on the weight of thepolystyrene homopolymer or copolymer (inclusive of solid and, if any,liquid additives, but exclusive of propellant); wherein the silica andthe graphite are used in a weight ratio in a range of from 1:1.5 to1:10.
 6. The expandable polymer granulate of claim 1, wherein thegranulate is obtainable by a process comprising the following steps: i)providing continuously to a mass prepolymerization reactor (or the firstfrom a cascade of reactors) a stream of: i1) polystyrene homopolymer orcopolymer and optionally at least one comonomer, i2) at least oneadditive solution, and i3) optionally recycled monomer, ii) continuingpolymerization in the prepolymerization reactor or the sequence ofcascade reactors, iii) addition of athermanous fillers: a) silica and b)graphite, and optionally further additives, iv) degassing the polymer,v) feeding the polymer in molten state into the extruder, vi) optionallyadding a flame retardant system including synergist and thermalstabilisers, vii) injecting blowing agent, viii) extruding thehomogenous polymer blend, and ix) pelletizing in an underwaterpelletizer, so as to obtain the granulate, wherein a) the silica isamorphous and has a BET surface of from 1 to 100 m²/g, an averageparticle size in a range of from 3 nm to 1,000 nm, and the silica ispresent in an amount of from 0.01 to less than 2 wt. %, based on theweight of the polymer (inclusive of solid and, if any, liquid additives,but exclusive of propellant), and b) the graphite has a carbon contentin a range of from 50 to 99.99 wt. % and a particle size in a range offrom 0.01 to 100 μm, and the graphite is present in an amount in a rangeof from 0.01 to 10 wt. %, based on the weight of the polystyrenehomopolymer or copolymer (inclusive of solid and, if any, liquidadditives, but exclusive of propellant); wherein the silica and thegraphite are used in a weight ratio in a range of from 1:1.5 to 1:10,wherein the expandable polymer granulate further comprises one or moreadditives selected from s) powders of calcium phosphate, mineral withperovskite structure, geopolymer and geopolymer composite, and t) carbonblack, petroleum coke, graphitized carbon black, graphite oxides, andgraphene.